Not sure if others have this, but I find that I am often running out of space on the /dev/mtdblock6 device when I try to install all the packages that I need.
I just wanted to mention that it's really easy following the standard instructions on https://wiki.openwrt.org/doc/howto/extroot to move your / to the micro SD slot
/dev/mmcblk0p1 on /overlay
After doing this I just have a lot more space, and fewer worries about filling the root file system.
I also make a habit of downloading whichever appropriate "packages" folder from the stas2z builds from Yandex, and just upload them to a hard disk that I have attached to the WITI. Then just modify /etc/opkg/distfeeds.conf to read something like:
src/gz mtwrt_core file://mnt/sda2/yandex/packages
Now at least all the packages tied to the particular kernel and build work and can be installed directly.